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F. E. BASH. OPTICAL PYROMETRIC METHOD AND APPARATUS.

'APPLICATION FILED MAR- 29. 19I9.

Patented Dec. 14, 1920.

FICiZ.

A V5 WAVE LENGTH.

TRANSMISSION VS WAVE LENGTH IIVVENTOI? $5. @M 2 ATTORNEY.

A Ell 3 r my rear Pier :2. A

FRANCIS E H, on PIIIILADELPHIA, rsmxis'rnvama, Assmnos To LEEDS a m'os'rrmor commas-a, or PHILADELPHIA, rnnnsrnvsma, a CGRIQEA.

OPTICAL PYROIIEETRIC METHOD AND APPARJMTUS.

Specification of Letters Fatent.

Patented Dee, 114 "Rhfifi.

Application filed. March 28, 1919. Serial No. 285,92'5.

metric method and apparatus characterized by the employment in well known manner for the measurement of high temperatures of a standard of illumuiatlon, as an incandescent lamp filament, flame or equivalent, whose brightness is matched with the brightness of light transmitted from the glowing body whose temperature is to be determined through a light absorbing structure or screen, the brightness of the stand- '0 ard serving when a match s attained as an indication or measure of of the glowing; body.

lily invention resides in a method of optical pyrometry oi the character referred to the temperature 5 wherein the light. emitted by the glowing body and having components of many colors or wave lengths is selectively transmitted tl'irolilgh a color selective or unneutral 'al' sorption screen in such manner that the percentage of transmission of the absorp tion. screen increases proportiorultely with increase in wave length, particularly within a range ofwave lengths of which the ocular absorptionscreen behvecn the light ss'standard and the eye is selective; and in such manner that for all absolute ten'iperau tures of the body whose temperature is to be measuredpequiring the use of an absorb .ing screen, the reciprocal of the absolute temperature minus the reciprocal of tl'ie ap parent temperature or temperature of a light standard as afi'ected or determined by the absorbing screen, is constant.

My invention resides in optical pyrometric apparatus of the character referred to wherein the absorption screen interposed between the light standard and the body whose temperature is to be measured has the above mentioned characteristics, where 36 by not only a brightness match, as usual in optical pyrometry. is possible between the light source and. the light transmitted through the absorption screen, but also a color matchis attained. For the absorptwn proximately 2800 degrees F. a color screen may he used an unneutral colored glass of suitable characteristics,,or an unneutral or colored glass in combination with a substantially neutral li ht absorbing glass or other means; my prererred combination comprises, however, an unneutral or colored glass of suitable characteristics incombination avith another unneutral colored glass of suitable compensatory character istics. r

In optical pyrometry it has heretofore been the practice to employ an incandescent electric lamp or other light source in association with an eye-piece and an absorption screen between the lamp filament and the body whose temperature is to be measured, the screen serving as a means for increasing the range of the instrument beyond the temperatures at which itwould be possible, desirable or safe to run the lamp filament. in the absence of the absorption screen.

So far asl am aware, with the absorption screens heretofore employed in the relation above described, it has been necessary for procuring the calibration for the high temperaturerange ot the pyrometer nee/es sitating the use of the absorbing screen, to make experimental determinations respect ing the absorbing screen and thereafter makeinrolved caharlations, due to the fact that the A value of the screen varied with temperature.

In accordance with my invention, how ever, because of the proportionality between increasing -transmission of the absorption screen and increasing wave length, and because ot' the constancy of the so-called A alue of the screen, I am enabled more eas ily to calibrate an optical pyrometer of the character referred to for all temperatures above that necessitatinc the use of the screen, by simple determii'iationand calcu lationfrom the characteristics of the incandescent lamp or other standard used.

With 'o tical pyrometers heretofore employed, so far as'l am aware, inineasurinp; high temperatures,particularly above apmatch temperature-brightness v between the lamp filament or other standard with the light fronl the hot body passing through the absorption screen, has not been possible, with resultant introduction oi error in temperature measurements dueto judgment or characteristics of the eye of the observer, due to the act that the lamp filament would not, thoiurh at the same brightness. in eflect merge into the field illuminated by the transmitted light. By my absorption screen, however, a color match in addition to the match in brightnesu, is available througl'lout the high temperature range of the instrument.

For an understaruling 0t my invention reference is had to the acconnmnying drawing, in which:

Figure 1 is in part a sectional view and in part a diagrammatic View of connections of one of many forms of pyroinetric apparatus in. which my invention may be embodied.

Fig. 2 is a graphic. representation of optical characteristics of my absorption screen.

3 is a further graphic representation of optical characteristics of my absorption screen.

Referring to Fin. 1, 1 and 2 are telescopic tubes. At the front end of the tube 2 is mounted the objective lens The tube 1 is closed at its rear end by the member I} supporting the eye piece structure having the ocular lens 5 in front of which are (liS")O$5(l colored glass screens i and g. Suitably dis posed within the tube b is the incandescentlamp L having the filament F connected in circuit with the batte 'y or soiirce of current 6, rheostat or adjustable resistance. 7 and the Ulkrsonval or other galvanon'ieter or amnieter whose scale, generally in two ranges, may have a total range from 1200 to (55W) degrees F, or higher.

Between the lamp L and the objective 3 isidisposed the member or diaphragm 9 having the aperture in in the optical axis of the instrun'ient, in which axis also is the aperture 11 adjacent the eye piece structure.

Upon the member 5) pivoted at 12 the lever 13 having: a handle lit extending to the exterior of the telescca'ic structure; At its inner end the lever 13 carries the holder 15, in which are disposed the absorption screen. elcniei'its (i and i which may be. for example. and pret'cralny. clear, non-opalescent unneutral glasses color-ed, respectively, blue-green and purple. 'lfbe'screen is removable from operative position illustrated by actuating: the lever handle i i, as when relatively low temperatures are to be measurcd.

The apparatus described is used as well understood in the art by sighting through the telescope upon the incandescent body whose temperature is to be measured. Light from the body passes through the objebtive 3 through the absorption screen elements G and P and then with light from the filament F passes through the ocular screens g and r and lens 5 to the observers eye. The rheostar 7 is adjutcduntil the brightness of the filament F matches with the brightness of the illuminated field due to light from the incaiulescent body transmitted through the absorption screen. The temperature then becomes known by reading the deflection of the meter M whose-scale readings depend upon the characteristics of the particular lamp filament F employed.

When an absorption screen is employed between the lamp filament and the object whose temperature is to be measured, the temperature of" the filament I corresponding with a brightness match is the apparent tempe 'ature of the hot body; its real temperature is, however, higher, and is the temperature of the filament F increased by an amount dependent upon the transmission characteristics of the interposed absorption screen. The high range calibration of the a maratus, and particularly of the meter M. is=tlu refore dependent upon the transmission characteristics of the absorption screen. Such high range calibration can be calculated or determined from-the low range calibration, that is, the calibration of the filament F itself where no interposed screen is employed, only When'the transmission characteristics of the interposed screen are known.

1n the case of an incandescent or glowing body which is a so-called perfect'radiator, that 1s, which has black body characteristics, and where an absorption screen intervenes between the black body and the light standard, as the lamp filament, the relation between the t 'ansmission of the screen, wave length of light, the true and apparent absolute temperatures, is given by lViens law, which as follows:

' -532 J c )\-5 )i'r in which- J is the energ' radiated from a black body for wave length 1 and absolute temperature T.

C, is a contant.

X is the particular wave length selected.

0 is the base of the Napierian logarithms.

C is a constantzlehoOQ.

T is the absolute temperature of the black body.

If a hot black body is viewed through an absorption screen and a black body lamp filament is matched against its brightness, theenergy'from the lamp filament at temperature T, and hot body at temperature T, by .Viens law will herfor the lamp filament and -21 J C A-5 AT;

for the, hot body.

' to .70 micron.

Color match is pr cured when the effective wave length reaching the eye from the incandescent body through the transmission screen coincides with the effective wave length of the light from the filament at matching brightness. The use of an oculalr screen atl'ects both similarly, and therefore whether or not an ocular screen is employed, a color match is obtained. This is accomplished in accordance with my in: vention because with rising temperature of the hot body the efiective wave length of light therefrom becomes shorter, and with shorter eliective wave length the transmission of my absorbing screen becomes less for that wave length, but its total transmission for all ware lenr ths increases, 7

and when the filament is rought to a brightness match dependent upon the total transmission through the absorbing screen, the eilective length of the light from the filament is the same as the effective wave length transmitted from the hot body through the absorbing screen. This accords with the expression l zl i l R! in which i. is the effective wave length of the light transmitted, through my absorbing screen, and Tr is the total transmission for the same hot body temperature, upon which total transmission depends the temperature or brightness to which the lamp lilament must be brought for match in brightness.

the foregoing algebraic expression. with varyingeffective wave length A the higarithni of the total transmission may be made to vary in such manner that the product oi the etlcctivc wave length into the Log Tr logarithm of thctotal transmission is a constant. This is true in the relation in which my screen is employed, and thisrelation cannot obtain unless the A valve of the absorbing screen is a constant, which is a characteristic of my screen.

These optical characteristics of my screen will be understood by reference to Figs. 2 and 3.

in Fig. ordinates are percentages of transmission and abscissa: wave lengths or values of A.

in the eye piece there is assumed to be used a red glass screen, as 1', or a number of them. This ocular screen or combination of ocular screens will selectively transmit redlight, for exai'nple. of wave lengths .60 With such an ocular screen or combination i only and preferably do employ an absorbing screen (i, 1, Fig. 1, ol clear non-opalcsccnt blue-grown and purple glasses. The upper curve in Fig. is the transmissionovare length curve of the green grass. employed. while the middle through the high temperature range.

definite thicknesses of each ofthe green and purple glasses, but for other proportions the third curve for the combinationwill nevertheless be a straightlinc. The slope of the combination curve may be made anything suitable or desirable and is made such that the transmission of the combination of green and purple glasses decreases at suit able rate with decreasingwvave length, at least within the range of the wave lengths indicated. Because of this decrease in transmission, with rise in temperature of the black body, which is accompanied, as pro viously explained, by a shifting of the eifectii e ware length to ard the blue end of the spectrum, the transmission of the combined green and purple glasses compensates for the eliect of such wave length change with temperature rise, and the color of the field against which the filament F is to be matched becomes such that a perfect color match betweenv filament and field is possible From this follows reduction of'errors on the part of the observer, and in fact a color-blind person can make as accurate measurements of temperature as a person having a normal cye,.since color match is automatically obtained and brightness match is readily made. In Fig. 3 ordinates are A values in Log Tr= j i i (lint is values of T T, while abscissze are again values of 7. or wave lengths ol the same range as in Fig. 2.

The lower curve is that of the green glass referred to 'in connection with Fig. 2; the middle curve is that for the purple glass referred to in connection with Fig. 2; the upper or combination curve is to all intents and purposes a straight line parallel with the X axis and results from the simple addition, at each wave length, of the 0rdi hates of the purple and green curves. The significance of the curve of the combination is that for all wave lengths, particularly throughout the range at which the neeenez absorbing screen which compensates-s for' wave length change accompanying changes in temperature and luminoslty of she glowng black, body. flwo 01 more such absorbmg screens placed in series, 'euch consisting c purple and green glass of the characters erred to in connection with Figs. 2 and 3, will have a combined A value which is the sum of the A values of the two combinations, and therefore es the four component glasses.

In producing a. screen of the improved characteristics above described due allowance is made, in Well known manner, since the screen isto be used in air, for nonseleciive absorption for such component piece in the combination, regardless of its thickness.

Where two colored glasses, es purple and tion consistent with the temperature range of the instrument.

By way offexa nple merely, and. without limitation of my invention thereto, it may be stated. that with a red ocular S('.I'8QI1,'&S Coming high transmission red, one combination of glasses for my absorbing screen comprehended Witl'zin'niy invention con ists of purple optical glass Gr 5'5 GP in series with blue-green optical glass G 171lZ 'obltained from the Corning Glass Works, Q01 inc N. Y. A suitable ratio of thickness of the purple to the thickness of the green glass is 1.2. Ubviously, however, for (lifife'cent melts of either or both of these types of glasses, or their equivalents, the thickness ratios may Vei" but are readily determinahle.

While I have referred more particularly to a combination of green and purple glasses, and to a certain Wave length range forthe ocular scrcen,-it will be understood that my invention is not limited in these respects and thetothei than eyed screen may be QH1- ployed in the eye piece, and that other than green and purple glasseslmay be used in combination forming the associated absorbing screen. Y

Foiexamplc, glasses of other colors than green and purple may be combined, so long as their variations ofA values, with respect to wave length vary in such manner that.

their combination has a constant A value throughout a range of Wave lengths, particularly the range of Wave lengths of the associated'ocular absorbing screen, if any be employed. It is a further feature of any invention bi udly that the transmission wave length clnuacteristdcs oi the screen elements so vary -that the products of their transmissions at various wave lengths vary proportimiately with Wave length.

While by preference I employ two unneutral or colored glasses, it will he understood that my invention comprehends also the employment of only one colored or unneutml glass in combination with a substantially neutral glass.

, lVhile in generil a red glass or glasses will be usedas the absorbing screen in the eye piece structure, or generally, between the lamp filament and the observers eye, a screen or screens of other color or colors may be employed. When employing a red oculei screen, there may be used in combination therewith a glass of green or other color. -liluztever the color or thickness of such ad ditional' screen or other colored glass 0!: glasses used in combination with the red ocular screen, the readings of the meter M: will always be the same for the same tom'- perature of the hot body. This for the sea- -son that such additional green or other colored glass in the eye piece structure cues down the light from thehot body and from the lamp'filament Without aiieeting the be havior of the main absorbing screen in asse ciation with the lamp filament and the iced screensti'ucture in the eye piece. l i'ith such combination the behavior of the instrument as affected by the main. absorbing screen is not altered, it still being possible to produce the high temperature range calibration h extrapolation 01' calculation, to procure the color match, and in general to procure all the advantages inherent in, employment of an absorbing screen of the described characteristics.

While I have referred to the absorbing screen as made up of a plurality of pieces of glass of difiercnt colors, it will be understood that a single piece of glass having therein lilo I the same proportions of the same colors is liquid in substitution for one or more of the colored glasses herein referred to.

While it has been hereinbefore assumed 1.25

7 that a temperature of a black body is to be measured, it will he understood that the apparatus is suitable also for measuring temperatures of incandescent bodies w h1c vacymeterially from black body conditions,

suitable corrections in the readings of temperature being made in the same manner as heretofore practised. hen the filament .F

is of carbon it also has black body characteristics, which have been assumed in the foregoing explanation of my invention. 'However, filaments of tungsten or other materials may also be employed and corrections for variations thereof from black body conditions may be made. 7

What I claim is:

1-. In optical pyrometry, the method of .measurlng temperatures of "an incandescent lute temperature of said body and the reciprocal of the corresponding absolute tem perature oiiisaid standard.

2. In optical pyrolnetric apparatus, light absorbing means whose A value is constant for different wave lengths of light.

3. In optical pyrometric apparatus, light absorbing means comprising serially disposed absorbing media at least one of which is unncutral and colored, the A value of said media being constant throughout a range 0i wave lengths of light.

4. In optical pyrometric apparatus, light absorbing means comprising absorbing members of differ ent colors whose joint A value is constant throughout a range of wave lengths of light.

5. In optical pyrometric apparatus, light absorbing means comprising blue-green and purple absorbing members ,whose joint- A value is constant throughouta range ofwaw'e lengths of red light.

6. Optical pyromct-ric apparatus comprising a light standard of predetermined tem peraturebrightness characteristic, and an absorbing screen disposed between said standard and'the body whosetemperature is to be measured and comprising unneutral colored light absorbing means whose A value is constant for different wave lengths.

7. (lptical pyrometric apparatus comprising a light standard of predeterminial temmeasured and comprising unneutral colored perature-brightness clulracteristic, an ab sorbing screen disposed between said standard and the light em1tt1ng body whose temperature is to be measured, and a red ocular screen, said absorbing screen compris I ing unneutral colored light absorbing means lwhoso A value is constant for the different light transmitting members whose joint A value is constant for difi'erent Wave lengths.

9. Optical pyrometric apparatus compris-.

ing a light standard of predetermined ternperature-brightness characteristic, an absorbing screen disposed between said standard and'the light emitting body whose temperature is to be measured, and a colored ocular screen, absorbing screen comprising unneutral colored light transmitting members Whose joint A value is constant for the'wave lengths transmitted by said ocular screen.

10. Optical pyrometric apparatus com prising a. light standard of predetermined ilta temperature-brightness characteristic, an

absorbing screen disposed between said standlu-d. and the light emitting body Whose temperature is to be measured, red ocular screen, said absorbing screen comprising unneutral colored light transmitting members whose joint A value is constant for the wave lengths transmitted by said ocular screen. 1

11. Optical pyrom-etric apparatus comprising a light standard of predetermined. temperature-brightness characteristic, an absorbing screen disposed between said standard and the light emitting body whose temperature is to be measured, and a red ocular screen. said absorbing screen comprising unneutral green and purple light transmitting members whose joint A value is constant For the visible wave lengths trans mitted through said ocular screen.

12. Optical pyrometric apparatus comprising a light standard of predetermined temperature-brightness characteristic, an absorbing screen disposed between said standard and the lightemitting body whose temperature is tobe measured, and. an ocular screen having components of different colors, said absorbing screen comprising unneutral colored light absorl'iine means whose A value is constant for the difi'erent visible wave lengths transmitted through the ocular screen.

13. Optical pyrometric apparatus comprising a light standard of predetermined is constant 'for the visible Wave lengths transmitted through said ocular screen.

14. Optical pyrometric apparatus com- ,prising a light stnndal'd of predetermined temperature brightness characteristic, and an absorbing screen disposed between said standard and the light emitting body whose temperature is to be measured comprising a plurality of screens each comprising un' neutral colored light absorbing means, the A value of each of said screens being con stant for the same range of Wave lengths, the joint A value of said screens being ronstant for the same range of wave lengths.

In testimony whereof I have hereunto affixed my signature this 24 FRANCIS E. BASH.

day of March, 

